1. Field of the Invention
The present invention relates to an internal combustion engine equipped with a variable valve control system.
2. Description of the Background Art
There has been a conventional internal combustion engine (also referred to as an engine) designed to switch the valve actions by use of a rocker arm. The rocker arm is disposed to link an engine valve with first and second cams that serve the engine valve and is supported by a rocker-arm shaft swingably and slidably in the axial direction of the rocker-arm shaft. By sliding on the rocker-arm shaft in the axial direction, the rocker arm engages selectively with one of the two cams to switch the valve actions (see, for example, Patent Documents 1 and 2).
The variable valve control system of Patent Document 1 includes: a lock lever provided in the rocker arm to be swingable and engageable with a notch formed in the outer circumference of the rocker-arm shaft; and a plunger provided in the journal bearing of the cam shaft and configured to work with the timing cam formed on the camshaft. The lock lever, if engaging with the notch, restricts the sliding movement of the rocker arm, and the restriction is removed at predetermined timings.
The variable valve control system of Patent Document 2 includes: an engagement member swingably provided on the rocker arm; an engagement groove formed in the rocker-arm shaft; and a protruding portion formed on the bottom of the engagement groove. At a timing of an action of the rocker arm while the engine speed is faster than a predetermined speed, the protruding portion flips the engagement member up, thereby removing the restriction imposed, by the engagement of the engagement member with the engagement groove, on the sliding movement of the rocker arm.    [Patent Document 1] JP-A-62-711    [Patent Document 2] JP-A-62-184117
The variable valve control system of Patent Document 1 employs a cam mechanism to remove the restriction imposed by the lock lever on the sliding movement of the rocker arm, and thus is capable of removing the restriction on the sliding movement of the rocker at accurate timings. The use of the cam mechanism, however, tends to make the overall configuration of the system more intricate.
The variable valve control system of Patent Document 2, on the other hand, has a difficulty in removing the restriction on the sliding movement of the rocker arm at accurate timings, because the timings of removing the restriction imposed by the engagement member on the sliding movement of the rocker arm may vary depending on: the size of the protruding portion formed on the bottom of the engagement groove; the size and the weight of the rocker arm; and the biasing force given to the engagement member.
An object of the present invention, therefore, is providing an internal combustion engine equipped with a variable valve control system which switches the actions of an engine valve by sliding a rocker arm in the axial direction of the rocker-arm shaft and which is capable of removing the restriction on the sliding movement of the rocker arm at accurate timings while employing a non-intricate configuration.